Voice coil motor

ABSTRACT

A voice coil motor of the movable coil type comprising a stator including a permanent magnet. The stator produces a magnetic field. A movable element made of an armature coil is provided. The armature coil is formed into a coil-shape having a cavity portion. A reinforcing beam made of non-magnetic and highly rigid material is formed at a substantial center of the cavity portion.

TECHNICAL FIELD

The present invention relates to a movable coil type voice coil motorespecially used for a semiconductor related device, a machine tool andso forth.

BACKGROUND OF THE INVENTION

It is a mainstream that the voice coil motor is of the movable coil typein which the stator includes a permanent magnet, which becomes amagnetic field, and the movable element includes an armature coil.

Concerning the stator, the following two types are used.

(1) When a view is taken from the side, the stator is formed into anE-shape, and one end of the yoke is open, so that the movable elementcan be detached.

(2) When a view is taken from the side, the stator is formed into aθ-shape, and one end of the yoke is closed, so that the movable elementcan not be detached.

The movable element includes an air-core coil formed into a cylindricalshape or a square cylindrical shape. Alternatively, the movable elementincludes a coil wound round a non-magnetic thin bobbin made ofengineering plastics or light metal.

FIG. 4 is a projection drawing showing a voice coil motor of the priorart, the side of the stator of which is formed into the θ-shape, whereinFIG. 4( a) is a partially sectional front view, and FIG. 4( b) is a sideview.

In FIG. 4, the stator 41 includes: a yoke 42 made of iron; a permanentmagnet 43; and a center yoke 44. In many cases, the thin copper sheet 46is wound round the center yoke 44 so as to reduce inductance.

The movable element 47 includes: a coil 48; and a movable elementattaching member 49. In some cases, the movable element 47 includes abobbin 52 (shown in FIG. 5) round which the coil 48 is wound.

The movable element 47 is held by a bearing not shown capable of movinglinearly in the axial direction. When a DC current is made to flow inthe coil 48, the movable element 47 can be moved in the arroweddirection (shown in FIG. 4( a)) by the Fleming's left-hand rule. Whenthe polarity of the electric current is inverted, the moving directioncan be reversed.

However, the following problems are caused in the above voice coil motorof the prior art.

FIG. 5 is a perspective view of the movable element of the conventionalvoice coil motor. In FIG. 5, the thickness t of the coil 48 in the wirestacking direction greatly affects the magnetic circuit of the stator.Therefore, it is impossible to extremely reduce the thickness t of thecoil 48. Accordingly, the rigidity of the movable element relies on onlythe non-magnetic thin bobbin 52 or on varnish and impregnation resinapplied at the time of winding the coil. Therefore, the rigidity of themovable element is relatively low. This relatively low rigidity hindersimprovements in the control characteristic of the voice coil motor.

DISCLOSURE OF THE INVENTION

It is an object of the present invention to enhance the rigiditycharacteristic of a voice coil motor, which has been improved recently,without affecting a magnetic circuit.

In order to solve the above problems, the present invention described inclaim 1 provides a voice coil motor of the movable coil type including:a stator of a permanent magnet which becomes a magnetic field; and amovable element of an armature coil, wherein the armature coil is formedinto a coil-shape having a cavity portion, and a reinforcing beam madeof non-magnetic and highly rigid material is formed at a substantialcenter of the cavity portion. According to this constitution, therigidity of the movable element can be enhanced.

Further, the invention described in claim 2 provides a voice coil motorof the movable coil type including: a stator of a permanent magnet whichbecomes a magnetic field; and a movable element of an armature coil,wherein a highly rigid reinforcing member, the shape of which is thesame as the coil section, is arranged at an end face of the coil.

Furthermore, the invention described in claim 3 provides a voice coilmotor of the movable coil type including: a stator of a permanent magnetwhich becomes a magnetic field; and a movable element of an armaturecoil, wherein the armature coil is formed into a coil-shape having acavity portion, a reinforcing beam made of non-magnetic and highly rigidmaterial is formed at a substantial center of the cavity portion, and ahighly rigid reinforcing member, the shape of which is the same as thecoil section, is arranged at an end face of the coil.

According to the above constitution, the rigidity of the movable elementis highly enhanced.

The non-magnetic and highly rigid reinforcing beam arranged at thesubstantial center of the cavity portion of the coil is effective forpreventing the occurrence of crushing and twisting of the coil.

The highly rigid reinforcing members arranged on both end faces of thecoil are also effective for preventing the occurrence of crushing of thecoil. As a result, the rigidity of the movable coil can be enhanced.

As described above, the present invention provides a voice coil motor ofthe movable coil type including: a stator of a permanent magnet whichbecomes a magnetic field; and a movable element of an armature coil,wherein the armature coil is formed into a coil-shape having a cavityportion, a reinforcing beam made of non-magnetic and highly rigidmaterial is formed at a substantial center of the cavity portion, and ahighly rigid reinforcing member, the shape of which is the same as thecoil section, is arranged at an end face of the coil. Due to the aboveconstitution, the reinforcing beam and the reinforcing ring prevent thecoil from being deformed. Therefore, it is possible for the reinforcingbeam and the reinforcing ring to greatly contribute an enhancement ofthe rigidity of the movable coil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a projection drawing showing the entire voice coil motor ofthe first embodiment of the present invention, wherein FIG. 1( a) is aside view and FIG. 1( b) is a partially sectional front view. FIG. 2 isa perspective view showing a movable element of the voice coil motorillustrated in FIG. 1. FIG. 3 is a perspective view showing a movableelement of the voice coil motor of the second embodiment of the presentinvention. FIG. 4 is a projection drawing showing a voice coil motor ofthe prior art, the shape of the side of the stator of which is formedinto the θ-shape, wherein FIG. 4( a) is a partially sectional front viewand FIG. 4( b) is a side view. FIG. 5 is a perspective view of a movableelement of the voice coil motor shown in FIG. 4. FIG. 6 is a diagramshowing a result of measurement of the natural frequency of the movableelement of the embodiment of the present invention. FIG. 7 is a diagramshowing a result of measurement of the natural frequency of the movableelement of the prior art

BEST MODE FOR CARRYING OUT THE INVENTION

Referring the drawings, the present invention will be explained indetail as follows.

FIG. 1 is a projection drawing showing the entire voice coil motor ofthe first embodiment of the present invention, wherein FIG. 1( a) is aside view and FIG. 1( b) is a partially sectional front view. FIG. 2 isa perspective view showing a movable element of the voice coil motorillustrated in FIG. 1. In FIGS. 4 and 5 showing the prior art, themovable element is formed into a square-cylinder-shaped coil. However,in the embodiment shown in FIG. 1, the movable element is formed into acylindrical coil. This embodiment will be explained as follows.

In FIG. 1, reference numeral 1 is a stator, reference numeral 2 is ayoke, reference numeral 3 is a permanent magnet, reference numeral 4 isa center yoke, reference numeral 5 is a gap, reference numeral 6 is athin copper sheet, reference numeral 7 is a movable element, referencenumeral 8 is a coil, reference numeral 9 is a movable element attachingmember, reference numeral 10 is a reinforcing beam, and referencenumeral 11 is a reinforcing ring.

The stator 1 includes: a yoke 2, a permanent magnet 3, a center yoke 4and a thin copper sheet 6. According to the present invention, thecenter yoke 4 is divided into two portions so that the gap 5, whichbecomes a passage of the reinforcing beam 10, can be ensured.

The movable element 7 includes: a coil 8, a movable element attachingmember 9, a reinforcing beam 10 and a reinforcing ring 11. In thisembodiment, the movable element attaching member 9 also functions as ahighly rigid reinforcing member arranged on the coil end face.

The movable element attaching member 9, the reinforcing beam 10 and thereinforcing ring 11 are strongly fixed to the coil 8 by means ofadhesion or by means of varnish or impregnation resin applied at thetime of winding the coil.

As described above, according to the present embodiment, when thearmature coil (the movable element 7) is formed into a coil-shape havinga cavity portion and the reinforcing beam 10 made of non-magnetic andhighly rigid material is arranged at the substantial center of thecavity portion, deformation of the movable coil 8 is prevented by thereinforcing beam 10. Accordingly, the rigidity of the movable coil 8 canbe greatly enhanced.

When the highly rigid reinforcing member 11, the shape of which is thesame as the coil section, is arranged on the end face of the coil 8,deformation of the coil 8 can be prevented by the reinforcing beam 10and the reinforcing ring 11. Therefore, the rigidity of the movable coil8 can be greatly enhanced.

FIG. 3 is a perspective view showing a voice coil motor movable elementof the second embodiment of the present invention. In FIG. 3, referencenumeral 8′ is a movable element coil, reference numeral 10′ is areinforcing beam, and reference numeral 11′ is a reinforcing ring. Themovable element 7 includes: a coil 8′, a reinforcing beam 10′ and areinforcing ring 11′. These components are strongly fixed to the coil bymeans of adhesion or by means of varnish or impregnation resin appliedat the time of winding the coil. In the structure shown in FIG. 3, thereinforcing beam 10′ is extended in the stroke direction exceeding therange of the reinforcing rings 11′, 11′ and directly joined to a body tobe moved. Therefore, it is unnecessary to provide the movable elementattaching member 9 shown in FIG. 2.

Due to the above structure, the reinforcing beam 10 and the reinforcingring 11 prevent deformation of the coil 8. Therefore, the rigidity ofthe movable coil can be greatly enhanced.

In this connection, since the reinforcing beam 10 and the reinforcingring 11 prevent from deformation of the coil 8, rigidity of the movablecoil is highly enhanced. Therefore, the movable element ring 9 is madeof alumina ceramics, and the reinforcing beam 10 and the reinforcingring 11 are made of carbon fiber reinforced plastics (CFRP).

As described above, according to the present embodiment, when thearmature coil (the movable element 7′) is formed into a coil-shapehaving a cavity portion and the reinforcing beam 10′ made ofnon-magnetic and highly rigid material is provided at the substantialcenter of the cavity portion, the reinforcing beam 10′ preventsdeformation of the movable coil 8′. Accordingly, the rigidity of themovable coil 8′ can be greatly enhanced.

When the highly rigid reinforcing members 11′, 11′, the shapes of whichare the same as the coil section, are arranged on both end faces of thecoil 8′, the reinforcing beam 10′ and the reinforcing ring 11′ preventdeformation of the coil 8′. Therefore, the rigidity of the movable coilcan be greatly enhanced.

FIG. 6 is a diagram showing a result of natural frequency of the movableelement of the voice coil motor, to which the present invention isapplied, in free oscillation. In the diagram, the axis of ordinatesrepresents a gain, and the axis of abscissas represents a frequency.

FIG. 7 is a diagram showing a result of natural frequency of the movableelement of the voice coil motor of the prior art in free oscillation. Inthe diagram, the axis of ordinates represents a gain, and the axis ofabscissas represents a frequency.

When both are compared with each other, the following can be said. Themotor characteristics are approximately the same with each other.However, concerning the primary natural frequency, in the case where thepresent invention is applied, the primary natural frequency is 1275 Hz,and the maximum gain frequency is 2975 Hz, as shown in FIG. 6.

On the other hand, as shown in FIG. 7 which is related to the movableelement of the voice coil motor of the prior art, the primary naturalfrequency is 700 Hz, and the maximum gain frequency is 962.5 Hz.Accordingly, it can be understood that the rigidity of the movableelement of the voice coil motor (shown in FIG. 6) of the presentinvention is higher than the rigidity of the movable element of thevoice coil motor (shown in FIG. 7) of the prior art. However, in thiscase, since a force of excitation at the time of measurement in the caseof the movable element of the voice coil motor of the present inventionis different from a force of excitation at the time of measurement inthe case of the movable element of the voice coil motor of the priorart, it is impossible to compare the gain of the movable element of thevoice coil motor of the present invention with the gain of the movableelement of the voice coil motor of the prior art.

INDUSTRIAL APPLICABILITY

The present invention can be utilized for a field in which a voice coilmotor capable of enhancing the rigidity characteristic without affectingthe magnetic circuit is manufactured when the invention is applied to amovable coil type voice coil motor especially used for a semiconductorrelated device or a machine tool.

1. A voice coil motor of the movable coil type comprising: a statorcomprising a yoke divided into two portions forming a cylindrical spacetherein, and a permanent magnet mounted on an inside of the dividedyoke; and a movable element of an armature coil accommodated in thecylindrical space of the stator comprising: a highly rigid reinforcingmovable element attaching member attached to one end of the armaturecoil in the stroke direction and provided with a protrusion extendingacross a gap in the divided yoke, the member having the same shape as acoil section of the armature coil; a highly rigid reinforcing ringhaving the same shape as the coil section fixed at the other end of thearmature coil in the stroke direction; and a reinforcing beam made ofnon-magnetic and highly rigid which extends laterally inside thearmature coil from one side to the other through substantially thecenter of the coil and extends longitudinally in the stroke directionfrom the movable element attaching member to the reinforcing ring, thebeam fixed to the inside of the armature coil, radially inside theprotrusion of the movable element attaching member.